This invention relates to fingerprint sensing technology and more particularly to fingerprint sensing circuits that can be programmed with different sensing patterns.
Fingerprint sensing technology is increasingly recognized as a reliable, non-intrusive way to verify individual identity. Fingerprints, like various other biometric characteristics, are based on unalterable personal characteristics and thus are believed to be more reliable when identifying individuals. The potential applications for fingerprints sensors are myriad. For example, electronic fingerprint sensors may be used to provide access control in stationary applications, such as security checkpoints. Electronic fingerprint sensors may also be used to provide access control in portable applications, such as portable computers, personal data assistants (PDAs), cell phones, gaming devices, navigation devices, information appliances, data storage devices, and the like. Accordingly, some applications, particularly portable applications, may require electronic fingerprint sensing systems that are compact, highly reliable, and inexpensive.
Various electronic fingerprint sensing methods, techniques, and devices have been proposed or are currently under development. For example, optical and capacitive fingerprint sensing devices are currently on the market or under development. Like a digital camera, optical technology utilizes visible light to capture a digital image. In particular, optical technology may use a light source to illuminate an individual's finger while a charge-coupled device (CCD) captures an analog image. This analog image may then be converted to a digital image.
There are generally two types of capacitive fingerprint sensing technologies: passive and active. Both types of capacitive technologies utilize the same principles of capacitance to generate fingerprint images. Passive capacitive technology typically utilizes an array of plates to apply an electrical current to the finger. The voltage discharge is then measured through the finger. Fingerprint ridges will typically have a substantially greater discharge potential than valleys, which may have little or no discharge.
Active capacitive technology is similar to passive technology, but may require initial excitation of the epidermal skin layer of the finger by applying a voltage. Active capacitive sensors, however, may be adversely affected by dry or worn minutia, which may fail to drive the sensor's output amplifier. By contrast, passive sensors are typically capable of producing images regardless of contact resistance and require significantly less power.
One feature common to each of the above fingerprint-sensing technologies is that they typically use arrays of fingerprint sensing elements, or “pixels,” to sense a fingerprint. For example, optical technology may use an array of solid state pixels (e.g., a charge-coupled device) to detect a fingerprint, whereas capacitive technology may use an array of capacitive-type sensors, or “pixels.” Each of these pixels may interface with a fingerprint sensing circuit (e.g, a fingerprint-sensing IC) using pins, leads, or other interconnects. In certain cases, the pixels that are used for scanning, as well as the scanning sequence of the pixels, is fixed or difficult to change after the fingerprint-sensing circuit is designed and implemented. In certain cases, the pixels and their sequence may depend on which interconnects they connect to. This characteristic may limit the flexibility of the fingerprint sensing circuit.
Accordingly, it would be an advance in the art to provide a fingerprint sensing circuit with greater flexibility. Ideally, the sensing pattern of a fingerprint sensing circuit could be programmed to include different pixels or sequences of pixels. Such flexibility may allow a fingerprint-sensing circuit to be tailored to different applications or allow fingerprint sensing circuits to be optimized or improved after they have been designed and implemented.